The application proposes to develop a system in which structure/functional aspects of two human autoimmune antigens (the "D" and "E" proteins) can be investigated. The D and E proteins are Sm antigens, antibodies to which are produced by many patients with systemic lupus erythematosus. These proteins are components of several small nuclear RNAs U1,U2, U4/U6, and U5 which are essential components of the RNA splicing machinery of eucaryotic cells. Although the protein components of these complexes have been identified, their functional role and structural relationship with one another remains to be elucidated. The recent cloning and expression of these proteins now make it feasible to address such questions. Clones of these two proteins are available from collaborators and will be used to generate in vitro translation products. The specific goals are (1) to develop an in vivo assembly system in Xenopus Oocytes for snRNPs and their precursor core particles that will incorporate in vitro synthesized and injected human D and E proteins into Xenopus snRNPs and core proteins; (2) to identify, using in vitro mutagenesis, the protein domains that are require for their incorporation into the 6S core particles; and (3) to identify, again using in vitro mutagenesis, the protein domains require for the incorporation of the proteins into mature snRNP. These studies are intended to provide information that will establish the role of these clinically important antigens in snRNP assembly and structure. Future work will extend these studies to include an examination of the role of these proteins in the splicing process.